2 Answers
2

DON'T reduce tire pressure

In fact, the recommended thing to do here would be to increase tire pressure if there is more load expected on the vehicle.

Have a look at this tire pressure placard for the Nissan Qashqai as an example:

Under normal loads, the factory recommendation is that all tires should be inflated at 33 psi

Under max load (4-7 passengers, more luggage), the fronts should be inflated to 38 psi and the rears at 42 psi.

Of course, every vehicle model will have its own unique inflation requirements.

Why wouldn't reducing tire pressure work?

The pressure inside the tire helps it keep shape.

By adding more load on the vehicle, the sidewalls of the tire will sag assuming the amount of air inside the tires will not have changed, meaning the tires are more underinflated as a result. This should help explain why you need to add more air (higher pressure).

In the opposite scenario, if the tire pressures are boosted to the max case, reducing the load of the vehicle will render the tires overinflated.

Thanks Zaid! This is really helpful! Especially the second section. Saved me from doing the wrong thing. Just one followup question though: Do I still follow the same tire pressure given my tires are no longer the original set of tires from manufacturer?
– Jomar SevillejoDec 15 '15 at 10:33

@JomarSevillejo no change, as long as the tire size hasn't changed then there is no need to deviate from the vehicle manufacturer's recommendation
– ZaidDec 15 '15 at 11:06

Normally you check the tyre pressures with the vehicle empty (or as empty as you can make it) and the tyres are cold (i.e. you have not driven the vehicle or haven't driven it a significant distance). Set them to the correct pressure for the load you will carry and then load up.

As you load the car the pressure will increase slightly but should remain within the maximum pressure rating for your tyre.